Cancer prevention studies: past, present, and future directions.

In spite of extensive research on vitamins and diet, a consistent beneficial role of vitamin supplements, together with diet modification in human cancer prevention, has not been demonstrated. Published results of human intervention trials with vitamin supplements have been contradictory. This review critically, but briefly, evaluates (a) current concepts of human carcinogenesis, (b) effects of vitamins on biochemical parameters that are pertinent to cancer prevention, and (c) whether past or current protocols for intervention trials among high-risk populations adopt specific scientific rationales that are based on laboratory and human epidemiology studies. In addition, we propose a novel experimental design for intervention trials among high-risk human populations that is based on sound scientific principles derived from laboratory and human epidemiologic data on vitamins, diet, lifestyle, and cancer prevention. Such trials would answer a fundamental public health issue of today: Does supplementation with multiple vitamins, together with diet and lifestyle modifications, reduce the risk of cancer?